Methods and systems for adaptive cropping

ABSTRACT

A video decoder is configured to receive a bitstream including a first coded picture having a first resolution and a second coded picture having a second resolution, wherein the first coded picture is an intra-coded picture, parameters defining a cropping window. The decoder decodes the first coded picture and stores the first picture as a reference picture, determines a scaling factor from at least one parameter in the bitstream defining the first cropping window, determines a predictor for the second picture from the reference picture and the scaling factor, decodes the second coded picture using the predictor, and outputs for display the first picture as cropped in accordance with the parameters defining the cropping window.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/193,712, filed on Mar. 5, 2021, and entitled “METHODS AND SYSTEMS FORADAPTIVE CROPPING, and is a continuation of U.S. application Ser. No.17/193,671, filed on Mar. 5, 2021, and entitled “METHODS AND SYSTEMS FORADAPTIVE CROPPING, and is a continuation of U.S. application Ser. No.17/193,617, filed on Mar. 5, 2021, and entitled “METHODS AND SYSTEMS FORADAPTIVE CROPPING, each of which is a continuation of U.S. applicationSer. No. 17/091,052, filed on Nov. 6, 2020 and entitled “METHODS ANDSYSTEMS FOR ADAPTIVE CROPPING,” now U.S. Pat. No. 11,006,132, whichclaims the benefit of priority of U.S. Provisional Patent ApplicationSer. No. 62/932,597, filed on Nov. 8, 2019, and titled “METHODS ANDSYSTEMS FOR ADAPTIVE CROPPING.” Each of U.S. application Ser. No.17/193,712, U.S. application Ser. No. 17/193,671, U.S. application Ser.No. 17/193,617, U.S. application Ser. No. 17/091,052 and U.S.Provisional Patent Application Ser. No. 62/932,597 is incorporated byreference herein in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of videocompression. In particular, the present invention is directed to methodsand systems for adaptive cropping.

BACKGROUND

A video codec can include an electronic circuit or software thatcompresses or decompresses digital video. It can convert uncompressedvideo to a compressed format or vice versa. In the context of videocompression, a device that compresses video (and/or performs somefunction thereof) can typically be called an encoder, and a device thatdecompresses video (and/or performs some function thereof) can be calleda decoder.

A format of the compressed data can conform to a standard videocompression specification. The compression can be lossy in that thecompressed video lacks some information present in the original video. Aconsequence of this can include that decompressed video can have lowerquality than the original uncompressed video because there isinsufficient information to accurately reconstruct the original video.

There can be complex relationships between the video quality, the amountof data used to represent the video (e.g., determined by the bit rate),the complexity of the encoding and decoding algorithms, sensitivity todata losses and errors, ease of editing, random access, end-to-end delay(e.g., latency), and the like.

Motion compensation can include an approach to predict a video frame ora portion thereof given a reference frame, such as previous and/orfuture frames, by accounting for motion of the camera and/or objects inthe video. It can be employed in the encoding and decoding of video datafor video compression, for example in the encoding and decoding usingthe Motion Picture Experts Group (MPEG)'s advanced video coding (AVC)standard (also referred to as H.264). Motion compensation can describe apicture in terms of the transformation of a reference picture to thecurrent picture. The reference picture can be previous in time whencompared to the current picture, from the future when compared to thecurrent picture. When images can be accurately synthesized frompreviously transmitted and/or stored images, compression efficiency canbe improved.

SUMMARY OF THE DISCLOSURE

In an aspect, an encoder includes circuitry configured to receive avideo including a current frame, select a cropped sub-frame of thecurrent frame, signal in a bitstream the cropped sub-frame of thecurrent frame as a function of the initial block segment, wherein thecropped sub-frame is signaled using at least a vertical offset and atleast a horizontal offset, the at least a vertical offset includes ansps_conf_win_top_offset and an sps_conf_win_bottom offset, the at leasta horizontal offset includes an sps_conf_win_left_offset and ansps_conf_win_right_offset, and signal in the bitstream a scalingconstant associated with the cropped sub-frame.

In another aspect, a decoder is provided with circuitry configured toreceive a bitstream including: a first coded picture, wherein the firstcoded picture including at least one intra-predicted block; a secondcoded picture; a sequence parameter set associated with both the firstand second coded pictures, the sequence parameter set including a firstset of parameters defining a first cropping window; a first pictureparameter set associated with the first picture; and a second pictureparameter set associated with the second picture. The decoder is furtherconfigured to decode the first coded picture and store the first pictureas a reference picture. The decoder further determines a scaling factorfrom at least one parameter in the sequence parameter set defining thefirst cropping window and determines a predictor for the second picturefrom the reference picture and the scaling factor. The decoder maydecode the second coded picture using the predictor and output fordisplay the first picture as cropped in accordance with the first set ofparameters defining the first cropping window in the sequence parameterset.

The details of one or more variations of the subject matter describedherein are set forth in the accompanying drawings and the descriptionbelow. Other features and advantages of the subject matter describedherein will be apparent from the description and drawings, and from theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show aspectsof one or more embodiments of the invention. However, it should beunderstood that the present invention is not limited to the precisearrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is a block diagram illustrating an exemplary embodiment ofexisting cropping methods;

FIG. 2 is an illustration of an exemplary embodiment of a referenceframe and sub-frame;

FIG. 3 is an illustration of an exemplary embodiment of a referenceframe and sub-frame;

FIG. 4 is an illustration of an example reference frame and examplepredicted frame;

FIG. 5 is an illustration of an example reference frame and examplepredicted frame;

FIG. 6 is a process flow diagram illustrating an example processaccording to some implementations of the current subject matter;

FIG. 7 is a system block diagram illustrating an example decoder capableof decoding a bit stream according to some implementations of thecurrent subject matter;

FIG. 8 is a process flow diagram illustrating an example process ofencoding a video according to some implementations of the currentsubject matter;

FIG. 9 is a system block diagram illustrating an example video encoderaccording to some implementations of the current subject matter; and

FIG. 10 is a block diagram of a computing system that can be used toimplement any one or more of the methodologies disclosed herein and anyone or more portions thereof.

The drawings are not necessarily to scale and may be illustrated byphantom lines, diagrammatic representations and fragmentary views. Incertain instances, details that are not necessary for an understandingof the embodiments or that render other details difficult to perceivemay have been omitted.

DETAILED DESCRIPTION

In traditional video coding systems, video sequence is divided intogroups-of-pictures (GOP). Each GOP is self-contained in the sense oftemporal and spatial prediction. Usually, first picture in the group isused as a reference picture for the subsequent pictures. Temporal andspatial relationships between the pictures allow for the very efficientcompression using predictive coding.

In certain scenarios during the transmission of the video a need mayarise to crop frames to be decoded, for instance to reduce the bitratein order to facilitate continuous playback. In many currentstate-of-the-art encoders, cropping is managed by re-coding andre-sending a whole portion of the video known as group-of-pictures(GOP), which includes an intra-frame (I-frame) used as a reference, andinformation usable to predict other frames from the reference. Thisrequires sending the intra-frame (I-frame) which can incur additionalcosts, since those frames are responsible for the bulk of the bits inthe GOP. As an illustrative example, in scenarios where videotransmission system experiences sudden drop in available bandwidth, orwhere a consumer of the video is interested in certain region within thevideo picture, there may be a need to transmit and present given regionof interest within the video picture. Existing video coding systemsachieve this by discarding already transmitted portion of the video andre-encoding and re-sending new video. For example, as illustrated inFIG. 1 , both a first reference picture 104 a second reference picture108 may be encoded and transmitted 112. This is not only inefficient,but also induces delays on the decoder side which impair userexperience.

The current subject matter relates to systems and processes adaptivecropping, which is a technique that enables additional flexibility forthe video encoder/decoder allowing bitrate savings in various use cases.In general, adaptive cropping combines cropping as signaled in abitstream with adaptive scaling as signaled in the bitstream; adaptivecropping may include performing a prediction using a reference region ofa reference frame as a reference for a current frame, where thereference region “sub-frame” has an area, defined for instance inpixels, that is smaller than an area of the reference frame. In currentcoding standards, predicted frames are generated from entire referenceframes. In adaptive cropping, a reference region within a referenceframe can be used as a reference picture to generate the predictedframe. This approach can be used to downscale video resolution, thusreducing bitrate, to focus on a region of interest to a viewer, and/orto focus on a region identified by automated or user-facilitateddetection as containing visual data of greater relevance to some purposeand/or task.

In some embodiments, adaptive cropping may be used for any number offrames, at any position within GOP, thus removing the requirement forI-frame re-coding and/or retransmission.

Referring now to FIG. 2 , an exemplary embodiment of a frame 204, whichmay include a reference frame, with a sub-frame representing a croppedportion of the video view is illustrated. Sub-frame may be identified,for instance by a decoder as described in further detail below, withinreference frame. Sub-frame may be used as a reference region in a manneranalogous to the use of a cropped reference frame, without requiring acropped reference frame to be transmitted separately, to generate adecoded frame 208. Alternatively, a reference frame may be used withoutcropping to generate a current frame, which may be cropped and/orresized as described in further detail below, similarly withoutretransmission of a cropped reference frame. Advantages accruing to thisapproach may include saving bandwidth used for video transmission,saving resources used for video encoding, and/or saving time needed todecode and play the video. A result may be a superior user experience aswell as a more efficient use of resources in devices and/or networksimplementing disclosed embodiments.

As a non-limiting and illustrative example, and referring now to FIG. 3, reference frame may have a first resolution defined by a first widthD1 and a first height D2, where D1 and D2 may be, without limitation,numbers of units of measurement such as pixels and/or fractions ofpixels; an area of reference frame may be defined as an area of arectangular array of units of measurement D1 and D2, defined as aresolution D1×D2. Sub-frame 304 may have a width W and a height H,defining an area or resolution of W×H. Sub-frame 304 may define asub-picture within Reference picture that has same or smallerdimensions, where “smaller dimensions” signify that at least one of Wand H is smaller than a corresponding dimension of reference frame; inother words, either W is less than D1 or H is less than D2. As a result,resolution or area W×H may be less than resolution or area D1×D2.Sub-frame 304 may be defined by a quadruple (X,Y,W,H), where X,Y is thecoordinate of the top-left corner of the sub-frame 304 relative to thetop-left corner of the Reference picture, and W,H are width and heightof the sub-frame 304 expressed in the units of measurement. It should benoted that alternative quadruples may be selected to define sub-frame304, such as without limitation coordinates of an alternative corner ofsub-frame 304, a set of two diagonally opposed vertices, and/or vectorsto any defined points. Data defining sub-frame 304 may be static over aGOP; for instance, a quadruple (X,Y,W,H) or equivalent may be staticover a GOP. Alternatively, or additionally, data defining sub-frame 304may be dynamic. For example, and without limitation, sub-frame 304change between subsequent pictures of GOP to follow movement of anobject and/or person of interest in a video picture. Data may beprovided defining sub-frame 304 for each picture of group of pictures;this may be accomplished, without limitation, by a set of data definingsub-frame 304, for instance as described above, for each picture of agroup of pictures, by a set of data defining a sub-frame 304 in onepicture and further data describing movement of sub-frame 304 from onepicture to previous or subsequent picture, or the like. Data definingsub-frame 304 may be specified and/or signaled in a sequence parameterset (SPS); updated data defining sub-frame 304 may be provided in apicture parameter set (PPS) for one or more selected pictures and/orframes of a GOP.

Still referring to FIG. 3 , cropped sub-frame 304 may be signaled usingat least a vertical offset and at least a horizontal offset; forinstance, and without limitation, quadruple as described above mayspecify a vertical offset from a top edge of frame, a vertical offsetfrom a bottom edge of frame, a horizontal offset from a left edge offrame, and a horizontal offset from a right edge of frame, where offsetsmay be measured in pixels of a frame either prior to or after rescalingas described in further detail below. As a non-limiting example, atleast a vertical offset may include an sps_conf_win_top_offset and ansps_conf_win_bottom offset, which may be signaled in an SPS and mayidentify, respectively, a vertical offset from a top edge of frame and avertical offset from bottom edge of frame. As a further non-limitingexample, at least a horizontal offset may include ansps_conf_win_left_offset and an sps_conf_win_right_offset, which may besignaled in an SPS and may identify, respectively, a horizontal offsetfrom a left edge of frame and a horizontal offset from a right edge offrame.

With continued reference to FIG. 3 , a sub-frame 304 which may be usedas a cropped frame may alternatively or additionaly be identified byspecification of one or more tiles or slices to be included in and/orexcluded from the sub-frame 304. Tile number and position within a framemay be signaled in a picture header. In an embodiment, signaling may beexplicit; alternatively or additionally, PPS may signal tile rows,columns, row height, and/or column width, any or all of which may becombined and/or utilized by a decoder to determine tile count and/ornumber. For instance, and without limitation, a PPS parameter denoted aspps_num_exp_tile_columns_minus1, with 1 added to it, may specifie anumber of explicitly provided tile column widths. As a furthernon-limiting example, a parameter pps_tile_column_width_minus1[i], with1 added to it, may specify the width of the i-th tile column, forinstance in units of coding tree blocks (CTBs) for i in the range of 0to pps_num_exp_tile_columns_minus1, inclusive. A parameterpps_tile_row_height_minus1[i] plus 1, with 1 added to it, may specifythe height of the i-th tile row, for instance in units of CTBs for i.Signaled parameters may alternatively or additionally specify numbersand/or dimensions of slices within one or more tiles. For instance, aparameter denoted pps_num_exp_slices_in_tile[i] may specify a number ofexplicitly provided slice heights for slices in a tile containing thei-th slice. A parameter denoted pps_slice_width_in_tiles_minus1 [i],with 1 added to it, may specify a width of the i-th rectangular slice inunits of tile columns. A parameter denotedpps_slice_height_in_tiles_minus1[i], with 1 added to it, may specify aheight of the i-th rectangular slice in units of tile rows, for instancewhen pps_num_exp_slices_in_tile[i] is equal to 0. Persons skilled in theart, upon reviewing the entirety of this disclosure, will be aware ofvarious alternative or additional ways in which tile and/or sliceparameters may be signaled and/or determined in and/or from bitstreamand/or header parameters, whether implicitly or explictly.

Further referring to FIG. 3 , a frame may be divided into two or moresub-frames 304. Sub-frames 304 may be identified and/or signaled one ormore tiles and/or slices as described above, including, withoutlimitation, by specification of tiles and/or slices included in a givensub-frame 304. One or more such sub-frames 304 may be used as a croppedsub-frame 304 as described in this disclosure or excluded therefrom.

With continued reference to FIG. 3 , adaptive cropping may beimplemented as a mode. In case of adaptive cropping mode activation atsome point during decoding, a decoder may have already received areference frame at resolution D1×D2 and may select a subregion using aquadruple as described above. In some implementations, encoder maysignal to the decoder using extra bits in a bitstream. Signaling bitsmay a reference frame index and/or an index identifying a GOP, within abuffer identifying picture indices at a decoder, and a sub-frame 304quadruple. Decoder may then perform cropping operation on referencepicture as identified by index, and according to quadruple, andoptionally a scaling operation on the cropped sub-frame 304. Subsequentframes may be predicted from the cropped and optionally scaled sub-frame304, or, where sub-frame 304 is a frame decoded as a function ofreference frame, may be predicted from reference frame prior to croppingand optionally scaling. Where data defining sub-frame 304 is dynamic asdescribed above, subsequent frames may further be predicted using suchdata and a reference frame; advantageously, a single reference frame maybe used for a sub-frame 304 that moves relative to the reference frame,without requiring retransmission of the reference frame. Cropping and/orresizing may be performed on a reference frame itself prior to decodinga current frame using sub-frame 304; alternatively or additionally, acurrent frame may be decoded using reference frame and then croppedaccording to signaling as described above. Similarly, rescaling may beperformed on a reference frame and/or subframe prior to decoding of acurrent frame, or on a current frame subsequent to decoding.

Referring now to FIG. 4 , a decoder may implement adaptive cropping inone of a plurality of modes. In an exemplary embodiment, and asillustrated in FIG. 4 , a decoder may implement adaptive cropping usinga Reduced Resolution Mode (RRM). An RMM predicted picture may be of thesame resolution as sub-frame; for instance, where sub-frame is of asmaller resolution than reference frame, predicted picture may beprovided at the same, small resolution. In other words, cropped currentframe may retain a resolution of subframe without rescaling. Alloperations needed to obtain Predicted picture, such as prediction, maybe conducted on the region directly, and/or on reference frame prior tocropping. Predicted picture may subsequently be rescaled to a smaller orlarger picture.

With further reference to FIG. 4 , width and height of smaller andlarger frames may be obtained by multiplying reference width and heightby an arbitrary rescaling constant (Rc), also referred to as a scalingfactor and/or constant, which may alternatively or additionally bereferred to with a variable name such as RefPicScale. In case of smallerframes, Rc may have a value between 0 and 1. In case of larger frames,Rc may have a value greater than 1; for instance, Rc may have a valuebetween 1 and 4. Other values are possible. Rescaling constant may bedifferent for one resolution dimension than another; for instance, arescaling constant Rch may be used to rescale height, while anotherrescaling constant Rcw may be used to rescale width.

Still referring to FIG. 4 , rescaling may be implemented as a mode. Insome implementations, an encoder may signal to decoder which rescalingconstant to use, for instance as a function of a picture parameter suchas pps_pic_width_in_luma_samples parameter, apps_scaling_win_right_offset parameter, and/or apps_scaling_win_left_offset parameter. Signaling may be performed in asequence parameter set (SPS) corresponding to a GOP containing currentpicture and/or in a picture parameter set (PPS) corresponding to currentpicture. For instance, and without limitation, encoder may signalrescaled parameters using fields such as apps_pic_width_in_luma_samples, pps_pic_height_in_luma_samples,pps_scaling_win_left_offset, pps_scaling_win_right_offset,pps_scaling_win_top_offset, pps_scaling_win_bottom_offset, and/orsps_num_subpics_minus1. A parameter such aspps_scaling_window_explicit_signalling_flag equal to 1 may specify thatscaling window offset parameters are present in the PPS;pps_scaling_window_explicit_signalling_flag equal to 0 may indicate thatthe scaling window offset parameters are not present in the PPS. Whensps_ref_pic_resampling_enabled_flag is equal to 0, a value ofpps_scaling_window_explicit_signalling_flag may be equal to 0.pps_scaling_win_left_offset, pps_scaling_win_right_offset,pps_scaling_win_top_offset, and pps_scaling_win_bottom_offset mayspecify offsets that are applied to picture size for scaling ratiocalculation. When not present, values of pps_scaling_win_left_offset,pps_scaling_win_right_offset, pps_scaling_win_top_offset, andpps_scaling_win_bottom_offset may be inferred to be equal topps_conf_win_left_offset, pps_conf_win_right_offset,pps_conf_win_top_offset, and pps_conf_win_bottom_offset, respectively.

Further referring to FIG. 4 , W and H parameters as described above maybe represented, without limitation, using variables CurrPicScalWinWidthLand CurrPicScalWinHeightL, respectively; these variables may be derivedfrom signaled parameters as described above using one or moremathematical relationships between the signaled parameters and thevariables. For instance, and without limitation, CurrPicScalWinWidthLmay be derived according to the following equation:

CurrPicScalWinWidthL=pps_pic_width_in_luma_samples−SubWidthC*(pps_scaling_win_right_offset+pps_scaling_win_left_offset)

As a further non-limiting example, CurrPicScalWinHeightL may be derivedaccording to the following equation:

CurrPicScalWinWidthL=pps_pic_width_in_luma_samples−SubWidthC*(pps_scaling_win_right_offset+pps_scaling_win_left_offset)

Persons skilled in the art, upon reviewing the entirety of thisdisclosure, will be aware of various alternative computations that maybe used to derive the above-described variables. Encoder mayalternatively or additionally signal one or more such variables, Rc,Rch, and/or Rcw directly for instance and without limitation in a PPSand/or SPS.

Alternatively or additionally, and still referring to FIG. 4 , arescaling constant and/or set of rescaling constants as described abovemay be signaled in a bitstream using a reference to an index of a storedscaling constant and/or constants, and/or of a frame and/or block thatwas signaled using a previously signaled and/or utilized scalingconstant and/or constants. Reference to index of a stored scalingconstant may be signaled explicitly and/or determined from one or moreadditional parameters signaled in bitstream. For instance, and withoutlimitation, decoder may identify a reference frame and/or group ofpictures containing a current frame; where a rescaling constant haspreviously been signaled and/or used in such a group of pictures, with areference frame signaled as applicable to current frame and/or currentgroup of pictures, or the like, decoder may identify that rescalingconstant for use as a rescaling constant with the current frame.

In some implementations, and with continued reference to FIG. 4 ,rescaling operation may be executed on a block level of encoded framesand/or sub-frames. For example, a reference frame may first be rescaledand subsequently prediction may be performed. Block prediction processmay be performed on a scaled reference frame (having a scaledresolution) rather than the original reference frame. Rescalingreference frame may include rescaling according to any parametersignaled by an encoder as described above; for instance and withoutlimitation, where a reference frame to be used with current picture issignaled, such as via a reference to an index value associated withreference frame or the like, the signaled reference frame may berescaled, prior to prediction, according to any method of rescalingdescribed above. A rescaled reference frame may be stored in memoryand/or in a buffer, which may include without limitation a bufferidentifying frames contained therein by indices, according to whichframe retrieval may be performed; buffer may include a decoded picturebuffer (DCB) and/or one or more additional buffers implemented bydecoder. Prediction process may include, for example, inter pictureprediction including motion compensation.

Still referring to FIG. 4 , some implementations of block-basedrescaling may enable flexibility in applying optimal filters for eachblock, instead of applying same filter for a whole frame. In someimplementations, a skip-rescaling mode may be possible such that someblocks (based for example on the uniformity of the pixels and bitratecost) can be in a skip-rescaling mode (such that rescaling would notchange the bitrate). Skip-rescaling mode may be signaled in a bitstream;for instance, and without limitation, skip-rescaling mode may besignaled in a PPS parameter. Alternatively or additionally, decoder maydetermine that skip-rescaling mode is active based on one or moreparameters set by decoder and/or signaled in bitstream.

Still referring to FIG. 4 , spatial filters used in rescaling mayinclude, without limitation, bicubic spatial filters that apply bicubicinterpolation, bilinear spatial filters that apply bi-linearinterpretation, Lanczos filters that use Lanczos filtering and/orLanczos resampling using combinations of sinc filters, sinc-functioninterpolation and/or signal reconstruction techniques, or the like;persons skilled in the art, upon reviewing the entirety of thisdisclosure, will be aware of various filters that may be used forinterpolation consistently with this disclosure. Interpolation filtersmay include, as a non-limiting example, any filters described above, alow-pass filter, which may be used, without limitation, by way of anup-sampling process whereby pixels between pixels of block and/or frameprevious to scaling may be initialized to zero, and then populated withan output of the low-pass filter. Alternatively or additionally, anyluma sample interpolation filtering process may be used. Luma sampleinterpretation may include computation of an interpolated value at ahalf-sample interpolation filter index, falling between two consecutivesample values of a non-scaled sample array. Computation of interpolatedvalue may be performed, without limitation, by retrieval of coefficientsand/or weights from lookup tables; selection of lookup tables may beperformed as a function of motion models of coding units and/or scalingratio amounts, for instance as determined using scaling constants asdescribed above. Computation may include, without limitation, performingweighted sums of adjacent pixel values, where weights are retrieved fromlookup tables. Computed values may alternatively or additionally beshifted; for instance and without limitation, values may be shifted byMin(4, BitDepth−8), 6, Max(2, 14−BitDepth), or the like. Persons skilledin the art, upon reviewing the entirety of this disclosure, will beaware of various alternative or additional implementations that may beused for interpolation filters.

Referring now to FIG. 5 , a decoder may implement adaptive croppingusing a Same Resolution Mode (SRM). In SRM a sub-frame may be rescaled,for instance using a rescaling constant as described above, to match thefull resolution of the video; for instance, W and H may each bemultiplied by an Rc selected to scale W and H to the same size as D1 andD2 as described above, such as without limitation Rc=D1/W. Predictionand other operations may be performed to obtain predicted picture usingrescaled sub-frame.

Referring now to FIG. 6 , an exemplary embodiment of a method 600 ofadaptive cropping is disclosed. At step 605, a bit stream is received ata decoder. A current frame including a current block can be containedwithin a bit stream that the decoder receives. The bit stream caninclude, for example, data found in a stream of bits that is the inputto a decoder when using data compression. The bit stream can includeinformation necessary to decode a video. Receiving can includeextracting and/or parsing the block and associated signaling informationfrom the bit stream. In some implementations, the current block caninclude a coding tree unit (CTU), a coding unit (CU), or a predictionunit (PU).

At step 610, and with continued reference to FIG. 6 , a first frame isidentified using the bit stream. A cropped sub-frame of first frame isidentified as a function of the bitstream. Identifying the croppedsub-frame may include receiving, in the bitstream, a geometriccharacterization of the cropped sub-frame; this may be implemented inany manner described in this disclosure, such as without limitationquadruple such as (X,Y,W,H) as described above. Geometriccharacterization may include updates to data defining cropped sub-framewhere cropped sub-frame location relative reference frame is dynamic asdescribed above.

At step 615, and still referring to FIG. 6 , decoder determines ascaling constant associated with the cropped sub-frame as a function ofthe bitstream. This may be implemented, without limitation, as describedabove.

At step 620, and still referring to FIG. 6 , decoder reconstructs pixeldata of the cropped sub-frame using the scaling constant; this may beimplemented, without limitation, as described above.

Still referring to FIG. 6 , in some implementations, sub-frame may bedisplayed, for instance as a picture in a GOP.

In some implementations, and with continued reference to FIG. 6 , asecond frame or a portion thereof in an adaptive cropping mode and usingthe sub-frame as a reference frame. Decoding may include, withoutlimitation, decoding in RRM as described above, or in other wordsperforming decoding operations without rescaling the sub-frame. Decodingmay include, without limitation decoding in SRM as described above.Decoding may include generating a scaled reference frame using thescaled sub-frame and a scaling constant and decoding the second frame orportion thereof using the scaled reference frame.

FIG. 7 is a system block diagram illustrating an example decoder 700capable of adaptive cropping. Decoder 700 may include an entropy decoderprocessor 704, an inverse quantization and inverse transformationprocessor 708, a deblocking filter 712, a frame buffer 716, a motioncompensation processor 720 and/or an intra prediction processor 724.

In operation, and still referring to FIG. 7 , bit stream 728 may bereceived by decoder 700 and input to entropy decoder processor 704,which may entropy decode portions of bit stream into quantizedcoefficients. Quantized coefficients may be provided to inversequantization and inverse transformation processor 708, which may performinverse quantization and inverse transformation to create a residualsignal, which may be added to an output of motion compensation processor720 or intra prediction processor 724 according to a processing mode. Anoutput of the motion compensation processor 720 and intra predictionprocessor 724 may include a block prediction based on a previouslydecoded block. A sum of prediction and residual may be processed bydeblocking filter 712 and stored in a frame buffer 716.

In an embodiment, and still referring to FIG. 7 decoder 700 may includecircuitry configured to implement any operations as described above inany embodiment as described above, in any order and with any degree ofrepetition. For instance, decoder 700 may be configured to perform asingle step or sequence repeatedly until a desired or commanded outcomeis achieved; repetition of a step or a sequence of steps may beperformed iteratively and/or recursively using outputs of previousrepetitions as inputs to subsequent repetitions, aggregating inputsand/or outputs of repetitions to produce an aggregate result, reductionor decrement of one or more variables such as global variables, and/ordivision of a larger processing task into a set of iteratively addressedsmaller processing tasks. Decoder may perform any step or sequence ofsteps as described in this disclosure in parallel, such assimultaneously and/or substantially simultaneously performing a step twoor more times using two or more parallel threads, processor cores, orthe like; division of tasks between parallel threads and/or processesmay be performed according to any protocol suitable for division oftasks between iterations. Persons skilled in the art, upon reviewing theentirety of this disclosure, will be aware of various ways in whichsteps, sequences of steps, processing tasks, and/or data may besubdivided, shared, or otherwise dealt with using iteration, recursion,and/or parallel processing.

FIG. 8 is a process flow diagram illustrating an example process 800 ofencoding a video with adaptive cropping that can enable additionalflexibility for the video encoder/decoder allowing bitrate savings invarious use cases. At step 805, a video frame may undergo initial blocksegmentation, for example, using a tree-structured macro blockpartitioning scheme that can include partitioning a picture frame intoCTUs and CUs.

At step 810, and still referring to FIG. 8 , block-based adaptivecropping may be performed, including selection of a sub-frame of a frameor portion thereof. Region may be selected by the means of automatic orexpert input. Automatic selection may be achieved, as a non-limitingexample, by a computer vision algorithm that detecting certain objects;object detection may include further processing such as objectclassification or the like. Expert input selection may be achieved,without limitation, using human manual intervention, for exampleselecting a close-up of a person and/or object of interest in a video,such as a person in a surveillance video. Another possible use case maybe to select a maximally salient region that contributes the most to abit rate reduction. Adaptive cropping may further include selection of ageometric characterization of sub-frame; for instance, and withoutlimitation, selection of geometric characterization of sub-frame mayinclude selection of a quadruple as described above, such as withoutlimitation (X,Y,W,H). Selection of geometric characterization ofsub-frame may include updating information and/or information indicatingchanges to data defining sub-frame from one frame to another asdescribed above with regard to dynamic data defining sub-frame.

Still referring to FIG. 8 , at step 815, block may be encoded andincluded in the bit stream. Encoding can include utilizing interprediction and intra prediction modes, for example. Encoding may includeadding bits to the bitstream characterizing (X,Y,W,H), identifyingadaptive cropping mode, or the like, for instance as described above.Encoding may include encoding updating information and/or informationindicating changes to data defining sub-frame from one frame to anotheras described above with regard to dynamic data defining sub-frame. Inembodiments, encoder may determine and transmit a rescaling constant asdescribed above.

FIG. 9 is a system block diagram illustrating an example video encoder900 capable of adaptive cropping. Example video encoder 900 may receivean input video 904, which may be initially segmented or dividingaccording to a processing scheme, such as a tree-structured macro blockpartitioning scheme (e.g., quad-tree plus binary tree). An example of atree-structured macro block partitioning scheme may include partitioninga picture frame into large block elements called coding tree units(CTU). In some implementations, each CTU may be further partitioned oneor more times into a number of sub-blocks called coding units (CU). Afinal result of this portioning may include a group of sub-blocks thatmay be called predictive units (PU). Transform units (TU) may also beutilized.

Still referring to FIG. 9 , example video encoder 900 may include anintra prediction processor 908, a motion estimation/compensationprocessor 912, which may also be referred to as an inter predictionprocessor, capable of constructing a motion vector candidate listincluding adding a global motion vector candidate to the motion vectorcandidate list, a transform/quantization processor 916, an inversequantization/inverse transform processor 920, an in-loop filter 924, adecoded picture buffer 928, and/or an entropy coding processor 932. Bitstream parameters may be input to the entropy coding processor 932 forinclusion in the output bit stream 936.

In operation, and with continued reference to FIG. 9 , for each block ofa frame of input video 904, whether to process block via intra pictureprediction or using motion estimation/compensation may be determined.Block may be provided to intra prediction processor 908 or motionestimation/compensation processor 912. If block is to be processed viaintra prediction, intra prediction processor 908 may perform processingto output a predictor. If block is to be processed via motionestimation/compensation, motion estimation/compensation processor 912may perform processing including constructing a motion vector candidatelist including adding a global motion vector candidate to the motionvector candidate list, if applicable.

Further referring to FIG. 9 , a residual may be formed by subtracting apredictor from input video. Residual may be received bytransform/quantization processor 916, which may perform transformationprocessing (e.g., discrete cosine transform (DCT)) to producecoefficients, which may be quantized. Quantized coefficients and anyassociated signaling information may be provided to entropy codingprocessor 932 for entropy encoding and inclusion in output bit stream936. Entropy encoding processor 932 may support encoding of signalinginformation related to encoding a current block. In addition, quantizedcoefficients may be provided to inverse quantization/inversetransformation processor 920, which may reproduce pixels, which may becombined with a predictor and processed by in loop filter 924, an outputof which may be stored in decoded picture buffer 928 for use by motionestimation/compensation processor 912 that is capable of constructing amotion vector candidate list including adding a global motion vectorcandidate to the motion vector candidate list.

With continued reference to FIG. 9 , although a few variations have beendescribed in detail above, other modifications or additions arepossible. For example, in some implementations, current blocks mayinclude any symmetric blocks (8×8, 16×16, 32×32, 64×64, 128×128, and thelike) as well as any asymmetric block (8×4, 16×8, and the like).

In some implementations, and still referring to FIG. 9 , a quadtree plusbinary decision tree (QTBT) may be implemented. In QTBT, at a CodingTree Unit level, partition parameters of QTBT may be dynamically derivedto adapt to local characteristics without transmitting any overhead.Subsequently, at a Coding Unit level, a joint-classifier decision treestructure may eliminate unnecessary iterations and control the risk offalse prediction. In some implementations, LTR frame block update modemay be available as an additional option available at every leaf node ofQTBT.

In some implementations, and still referring to FIG. 9 , additionalsyntax elements may be signaled at different hierarchy levels ofbitstream. For example, a flag may be enabled for an entire sequence byincluding an enable flag coded in a Sequence Parameter Set (SPS).Further, a CTU flag may be coded at a coding tree unit (CTU) level.

Some embodiments may include non-transitory computer program products(i.e., physically embodied computer program products) that storeinstructions, which when executed by one or more data processors of oneor more computing systems, cause at least one data processor to performoperations herein.

Still referring to FIG. 9 , encoder 900 may include circuitry configuredto implement any operations as described above in reference to FIG. 8 or9 in any embodiment, in any order and with any degree of repetition. Forinstance, encoder 900 may be configured to perform a single step orsequence repeatedly until a desired or commanded outcome is achieved;repetition of a step or a sequence of steps may be performed iterativelyand/or recursively using outputs of previous repetitions as inputs tosubsequent repetitions, aggregating inputs and/or outputs of repetitionsto produce an aggregate result, reduction or decrement of one or morevariables such as global variables, and/or division of a largerprocessing task into a set of iteratively addressed smaller processingtasks. Encoder 900 may perform any step or sequence of steps asdescribed in this disclosure in parallel, such as simultaneously and/orsubstantially simultaneously performing a step two or more times usingtwo or more parallel threads, processor cores, or the like; division oftasks between parallel threads and/or processes may be performedaccording to any protocol suitable for division of tasks betweeniterations. Persons skilled in the art, upon reviewing the entirety ofthis disclosure, will be aware of various ways in which steps, sequencesof steps, processing tasks, and/or data may be subdivided, shared, orotherwise dealt with using iteration, recursion, and/or parallelprocessing.

With continued reference to FIG. 9 , non-transitory computer programproducts (i.e., physically embodied computer program products) may storeinstructions, which when executed by one or more data processors of oneor more computing systems, causes at least one data processor to performoperations, and/or steps thereof described in this disclosure, includingwithout limitation any operations described above in reference to FIGS.6 and 8 and/or any operations decoder 700 and/or encoder 900 may beconfigured to perform. Similarly, computer systems are also describedthat may include one or more data processors and memory coupled to theone or more data processors. The memory may temporarily or permanentlystore instructions that cause at least one processor to perform one ormore of the operations described herein. In addition, methods can beimplemented by one or more data processors either within a singlecomputing system or distributed among two or more computing systems.Such computing systems can be connected and can exchange data and/orcommands or other instructions or the like via one or more connections,including a connection over a network (e.g. the Internet, a wirelesswide area network, a local area network, a wide area network, a wirednetwork, or the like), via a direct connection between one or more ofthe multiple computing systems, or the like.

Embodiments disclosed herein include a decoder including circuitryconfigured to receive a bit stream, identify, as a function of thebitstream, a current frame, and a cropped sub-frame of the currentframe, determine, as a function of the bitstream, a scaling constantassociated with the cropped sub-frame, and reconstruct pixel data of thecropped sub-frame using the scaling constant.

In embodiments, the cropped sub-frame may be signaled in the bitstream.The cropped sub-frame may be signaled in a sequence parameter set (SPS).The cropped sub-frame may be signaled using at least a vertical offsetand at least a horizontal offset. The at least a vertical offset mayinclude an sps_conf_win_top_offset and an sps_conf_win_bottom offset andthe at least a horizontal offset may include an sps_conf_win_left_offsetand an sps_conf_win_right_offset. The scaling constant may include avertical scaling component and a horizontal scaling component. Thescaling constant may be signaled within the bit stream. The scalingconstant is signaled in a picture parameter set (PPS). The scalingconstant may be signaled as a function of apps_pic_width_in_luma_samples parameter, a pps_scaling_win_right_offsetparameter, and a pps_scaling_win_left_offset parameter. The decoder maybe configured to scale the cropped sub-frame by interpolating pixelvalues.

In an embodiment, a includes receiving, by a decoder, a bit stream,identifying, by the decoder and as a function of the bitstream, acurrent frame, and a cropped sub-frame of the current frame,determining, by the decoder and as a function of the bitstream, ascaling constant associated with the cropped sub-frame, andreconstructing, by the decoder, pixel data of the cropped sub-frameusing the scaling constant.

In embodiments, the cropped sub-frame may be signaled in the bitstream.The cropped sub-frame may be signaled in a sequence parameter set (SPS).The cropped sub-frame may be signaled using at least a vertical offsetand at least a horizontal offset. The at least a vertical offset mayinclude an sps_conf_win_top_offset and an sps_conf_win_bottom offset andthe at least a horizontal offset may include an sps_conf_win_left_offsetand an sps_conf_win_right_offset. The scaling constant may include avertical scaling component and a horizontal scaling component. Thescaling constant may be signaled within the bit stream. The scalingconstant is signaled in a picture parameter set (PPS). The scalingconstant may be signaled as a function of apps_pic_width_in_luma_samples parameter, a pps_scaling_win_right_offsetparameter, and a pps_scaling_win_left_offset parameter. The decoder maybe configured to scale the cropped sub-frame by interpolating pixelvalues.

It is to be noted that any one or more of the aspects and embodimentsdescribed herein may be conveniently implemented using digitalelectronic circuitry, integrated circuitry, specially designedapplication specific integrated circuits (ASICs), field programmablegate arrays (FPGAs) computer hardware, firmware, software, and/orcombinations thereof, as realized and/or implemented in one or moremachines (e.g., one or more computing devices that are utilized as auser computing device for an electronic document, one or more serverdevices, such as a document server, etc.) programmed according to theteachings of the present specification, as will be apparent to those ofordinary skill in the computer art. These various aspects or featuresmay include implementation in one or more computer programs and/orsoftware that are executable and/or interpretable on a programmablesystem including at least one programmable processor, which may bespecial or general purpose, coupled to receive data and instructionsfrom, and to transmit data and instructions to, a storage system, atleast one input device, and at least one output device. Appropriatesoftware coding may readily be prepared by skilled programmers based onthe teachings of the present disclosure, as will be apparent to those ofordinary skill in the software art. Aspects and implementationsdiscussed above employing software and/or software modules may alsoinclude appropriate hardware for assisting in the implementation of themachine executable instructions of the software and/or software module.

Such software may be a computer program product that employs amachine-readable storage medium. A machine-readable storage medium maybe any medium that is capable of storing and/or encoding a sequence ofinstructions for execution by a machine (e.g., a computing device) andthat causes the machine to perform any one of the methodologies and/orembodiments described herein. Examples of a machine-readable storagemedium include, but are not limited to, a magnetic disk, an optical disc(e.g., CD, CD-R, DVD, DVD-R, etc.), a magneto-optical disk, a read-onlymemory “ROM” device, a random access memory “RAM” device, a magneticcard, an optical card, a solid-state memory device, an EPROM, an EEPROM,Programmable Logic Devices (PLDs), and/or any combinations thereof. Amachine-readable medium, as used herein, is intended to include a singlemedium as well as a collection of physically separate media, such as,for example, a collection of compact discs or one or more hard diskdrives in combination with a computer memory. As used herein, amachine-readable storage medium does not include transitory forms ofsignal transmission.

Such software may also include information (e.g., data) carried as adata signal on a data carrier, such as a carrier wave. For example,machine-executable information may be included as a data-carrying signalembodied in a data carrier in which the signal encodes a sequence ofinstruction, or portion thereof, for execution by a machine (e.g., acomputing device) and any related information (e.g., data structures anddata) that causes the machine to perform any one of the methodologiesand/or embodiments described herein.

Examples of a computing device include, but are not limited to, anelectronic book reading device, a computer workstation, a terminalcomputer, a server computer, a handheld device (e.g., a tablet computer,a smartphone, etc.), a web appliance, a network router, a networkswitch, a network bridge, any machine capable of executing a sequence ofinstructions that specify an action to be taken by that machine, and anycombinations thereof. In one example, a computing device may includeand/or be included in a kiosk.

FIG. 8 shows a diagrammatic representation of one embodiment of acomputing device in the exemplary form of a computer system 800 withinwhich a set of instructions for causing a control system to perform anyone or more of the aspects and/or methodologies of the presentdisclosure may be executed. It is also contemplated that multiplecomputing devices may be utilized to implement a specially configuredset of instructions for causing one or more of the devices to performany one or more of the aspects and/or methodologies of the presentdisclosure. Computer system 800 includes a processor 804 and a memory808 that communicate with each other, and with other components, via abus 812. Bus 812 may include any of several types of bus structuresincluding, but not limited to, a memory bus, a memory controller, aperipheral bus, a local bus, and any combinations thereof, using any ofa variety of bus architectures.

Memory 808 may include various components (e.g., machine-readable media)including, but not limited to, a random-access memory component, a readonly component, and any combinations thereof. In one example, a basicinput/output system 816 (BIOS), including basic routines that help totransfer information between elements within computer system 800, suchas during start-up, may be stored in memory 808. Memory 808 may alsoinclude (e.g., stored on one or more machine-readable media)instructions (e.g., software) 820 embodying any one or more of theaspects and/or methodologies of the present disclosure. In anotherexample, memory 808 may further include any number of program modulesincluding, but not limited to, an operating system, one or moreapplication programs, other program modules, program data, and anycombinations thereof.

Computer system 800 may also include a storage device 824. Examples of astorage device (e.g., storage device 824) include, but are not limitedto, a hard disk drive, a magnetic disk drive, an optical disc drive incombination with an optical medium, a solid-state memory device, and anycombinations thereof. Storage device 824 may be connected to bus 812 byan appropriate interface (not shown). Example interfaces include, butare not limited to, SCSI, advanced technology attachment (ATA), serialATA, universal serial bus (USB), IEEE 1394 (FIREWIRE), and anycombinations thereof. In one example, storage device 824 (or one or morecomponents thereof) may be removably interfaced with computer system 800(e.g., via an external port connector (not shown)). Particularly,storage device 824 and an associated machine-readable medium 828 mayprovide nonvolatile and/or volatile storage of machine-readableinstructions, data structures, program modules, and/or other data forcomputer system 800. In one example, software 820 may reside, completelyor partially, within machine-readable medium 828. In another example,software 820 may reside, completely or partially, within processor 804.

Computer system 800 may also include an input device 832. In oneexample, a user of computer system 800 may enter commands and/or otherinformation into computer system 800 via input device 832. Examples ofan input device 832 include, but are not limited to, an alpha-numericinput device (e.g., a keyboard), a pointing device, a joystick, agamepad, an audio input device (e.g., a microphone, a voice responsesystem, etc.), a cursor control device (e.g., a mouse), a touchpad, anoptical scanner, a video capture device (e.g., a still camera, a videocamera), a touchscreen, and any combinations thereof. Input device 832may be interfaced to bus 812 via any of a variety of interfaces (notshown) including, but not limited to, a serial interface, a parallelinterface, a game port, a USB interface, a FIREWIRE interface, a directinterface to bus 812, and any combinations thereof. Input device 832 mayinclude a touch screen interface that may be a part of or separate fromdisplay 836, discussed further below. Input device 832 may be utilizedas a user selection device for selecting one or more graphicalrepresentations in a graphical interface as described above.

A user may also input commands and/or other information to computersystem 800 via storage device 824 (e.g., a removable disk drive, a flashdrive, etc.) and/or network interface device 840. A network interfacedevice, such as network interface device 840, may be utilized forconnecting computer system 800 to one or more of a variety of networks,such as network 844, and one or more remote devices 848 connectedthereto. Examples of a network interface device include, but are notlimited to, a network interface card (e.g., a mobile network interfacecard, a LAN card), a modem, and any combination thereof. Examples of anetwork include, but are not limited to, a wide area network (e.g., theInternet, an enterprise network), a local area network (e.g., a networkassociated with an office, a building, a campus or other relativelysmall geographic space), a telephone network, a data network associatedwith a telephone/voice provider (e.g., a mobile communications providerdata and/or voice network), a direct connection between two computingdevices, and any combinations thereof. A network, such as network 844,may employ a wired and/or a wireless mode of communication. In general,any network topology may be used. Information (e.g., data, software 820,etc.) may be communicated to and/or from computer system 800 via networkinterface device 840.

Computer system 800 may further include a video display adapter 852 forcommunicating a displayable image to a display device, such as displaydevice 836. Examples of a display device include, but are not limitedto, a liquid crystal display (LCD), a cathode ray tube (CRT), a plasmadisplay, a light emitting diode (LED) display, and any combinationsthereof. Display adapter 852 and display device 836 may be utilized incombination with processor 804 to provide graphical representations ofaspects of the present disclosure. In addition to a display device,computer system 800 may include one or more other peripheral outputdevices including, but not limited to, an audio speaker, a printer, andany combinations thereof. Such peripheral output devices may beconnected to bus 812 via a peripheral interface 856. Examples of aperipheral interface include, but are not limited to, a serial port, aUSB connection, a FIREWIRE connection, a parallel connection, and anycombinations thereof.

The foregoing has been a detailed description of illustrativeembodiments of the invention. Various modifications and additions can bemade without departing from the spirit and scope of this invention.Features of each of the various embodiments described above may becombined with features of other described embodiments as appropriate inorder to provide a multiplicity of feature combinations in associatednew embodiments. Furthermore, while the foregoing describes a number ofseparate embodiments, what has been described herein is merelyillustrative of the application of the principles of the presentinvention. Additionally, although particular methods herein may beillustrated and/or described as being performed in a specific order, theordering is highly variable within ordinary skill to achieve embodimentsas disclosed herein. Accordingly, this description is meant to be takenonly by way of example, and not to otherwise limit the scope of thisinvention.

In the descriptions above and in the claims, phrases such as “at leastone of” or “one or more of” may occur followed by a conjunctive list ofelements or features. The term “and/or” may also occur in a list of twoor more elements or features. Unless otherwise implicitly or explicitlycontradicted by the context in which it is used, such a phrase isintended to mean any of the listed elements or features individually orany of the recited elements or features in combination with any of theother recited elements or features. For example, the phrases “at leastone of A and B;” “one or more of A and B;” and “A and/or B” are eachintended to mean “A alone, B alone, or A and B together.” A similarinterpretation is also intended for lists including three or more items.For example, the phrases “at least one of A, B, and C;” “one or more ofA, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, Balone, C alone, A and B together, A and C together, B and C together, orA and B and C together.” In addition, use of the term “based on,” aboveand in the claims is intended to mean, “based at least in part on,” suchthat an unrecited feature or element is also permissible.

The subject matter described herein can be embodied in systems,apparatus, methods, and/or articles depending on the desiredconfiguration. The implementations set forth in the foregoingdescription do not represent all implementations consistent with thesubject matter described herein. Instead, they are merely some examplesconsistent with aspects related to the described subject matter.Although a few variations have been described in detail above, othermodifications or additions are possible. In particular, further featuresand/or variations can be provided in addition to those set forth herein.For example, the implementations described above can be directed tovarious combinations and sub-combinations of the disclosed featuresand/or combinations and sub-combinations of several further featuresdisclosed above. In addition, the logic flows depicted in theaccompanying figures and/or described herein do not necessarily requirethe particular order shown, or sequential order, to achieve desirableresults. Other implementations may be within the scope of the followingclaims.

What is claimed is:
 1. A decoder, the decoder comprising circuitryconfigured to: receive a bitstream the bitstream including: a firstcoded picture, wherein the first coded picture including at least oneintra-predicted block; a second coded picture; a sequence parameter setassociated with both the first and second coded pictures, the sequenceparameter set including a first set of parameters defining a firstcropping window; a first picture parameter set associated with the firstpicture; and a second picture parameter set associated with the secondpicture; decode the first coded picture and store the first picture as areference picture; determine a scaling factor from at least oneparameter in the sequence parameter set defining the first croppingwindow; determine a predictor for the second picture from the referencepicture and the scaling factor; decode the second coded picture usingthe predictor; and output for display the first picture as cropped inaccordance with the first set of parameters defining the first croppingwindow in the sequence parameter set.
 2. The decoder of claim 1,wherein: the second picture parameter set includes a second set ofparameters different from the first set of parameters and defining asecond cropping window; the second picture is decoded and stored as asecond reference picture; a second scaling factor is determined from atleast one parameter in the second set of parameters; and a secondpredictor is determined from the second reference picture and the secondscaling factor.
 3. The decoder of claim 1, wherein the first set ofparameters comprise a plurality of values from which four corners of arectangular cropping window can be determined.
 4. The decoder of claim1, wherein the first set of parameters defining a first cropping windowcomprise a top offset, a bottom offset, a left offset and a rightoffset.
 5. The decoder of claim 1, wherein the first coded picture has afirst resolution, the second coded picture has a second resolution, andthe first resolution is smaller than the second resolution.
 6. Thedecoder of claim 1, wherein the first coded picture has a firstresolution, the second coded picture has a second resolution, and thefirst resolution is larger than the second resolution.
 7. The decoder ofclaim 1, further comprising: an entropy decoder processor configured toreceive the bit stream and decode the bitstream into quantizedcoefficients; an inverse quantization and inverse transformationprocessor configured to process the quantized coefficients includingperforming an inverse discrete cosine; a deblocking filter; a framebuffer; and an intra prediction processor.
 8. A decoder configured to:receive a bitstream, the bitstream including: a first coded picturehaving a first resolution and a second coded picture having a secondresolution, wherein the first coded picture including at least oneintra-predicted block; a sequence parameter set associated with both thefirst and second coded pictures, the sequence parameter set including afirst set of parameters defining a first cropping window; a firstpicture parameter set associated with the first picture; and a secondpicture parameter set associated with the second picture; decode thefirst coded picture and store the first picture as a reference picture;determine a scaling factor from at least one parameter in the sequenceparameter set defining the first cropping window; determine a predictorfor the second picture from the reference picture and the scalingfactor; decode the second coded picture using the predictor; and outputfor display the first picture as cropped in accordance with the firstset of parameters defining the first cropping window in the sequenceparameter set.
 9. The decoder of claim 8 wherein: the second pictureparameter set includes a second set of parameters different from thefirst set of parameters and defining a second cropping window; thesecond picture is decoded and stored as a second reference picture; asecond scaling factor is determined from at least one parameter in thesecond set of parameters; and a second predictor is determined from thesecond reference picture and the second scaling factor.
 10. The decoderof claim 9, wherein the first set of parameters comprise a plurality ofvalues from which four corners of a rectangular cropping window can bedetermined.
 11. The decoder of claim 9, wherein the first set ofparameters defining a first cropping window comprise a top offset, abottom offset, a left offset and a right offset.
 12. The decoder ofclaim 8 wherein the first resolution is smaller than the secondresolution.
 13. The decoder of claim 8 wherein the second resolution issmaller than the first resolution.